Fix implausible event durations

[WolfgangFahl]

OPENRESEARCH conference durations

query

select count(*),endDate-startdate+1 as duration from 
event_orclone
where endDate is not Null and startDate is not Null
group by duration
order by 2 

result

count(*)	duration
1	-49
1	-43
3	-9
1	-7
1	-3
1	-2
2	-1
2	0
8522	1
14	2
2	3
1	17
1	40
1	46
2	48

[WolfgangFahl]

url	duration
ICTAC%202020	-49
ICS%202014	-43
AAAI%201994	-9
CCS%201998	-9
ICCV%201998	-9
Persuasive%202019	-7
CHI%202007	-3
ICWE%202013	-2
NAS%202009	-1
POPL%202010	-1
ECML%202000	17
ECDL%202009	40
ISMAR%202015	46
ESR%20-%207-8%202017%20%3A%20European%20Science%20Review%20Journal%207-8/2017	48
EuroCrypt%202017	48